Two Registry of Motor Vehicles officials and a service station owner pleaded not guilty to charges of extortion and fraud after allegedly scheming to create a “black market” for motor vehicle safety inspection licenses, US Attorney Carmen M. Ortiz and Boston FBI Special Agent Richard DesLauriers said Wednesday. David P. Gaw, 70, of Wakefield; Mark C. LaFrance, 51, of Braintree; and Simon Abou Raad, 50, of Tyngsborough, are accused of working to extort service station owners who wanted a license to conduct motor vehicle safety inspections, prosecutors said. LaFrance, a project manager at the Registry, allegedly gave Abou Raad a list of vehicle inspection stations with a low volume of inspections or that were planning to surrender licenses and sell equipment, enabling Abou Raad to buy the license and equipment for roughly $6,000. He then sold the licenses and equipment to other service station owners looking to buy licenses, sometimes with Gaw’s help, for between $50,000 and $75,000, prosecutors said.Lauren Dezenski can be reached at firstname.lastname@example.org. Follow her on Twitter @LaurenDezenski.